1. Field of the Invention
The present invention relates to a coating film forming apparatus comprising a spincoater for feeding a coating solution onto a substrate to be coated and rotating the substrate to be coated, thereby forming a desired film.
2. Description of the Related Art
Examples of a method for forming a coating film having a uniform thickness on a substrate to be coated such as a semiconductor wafer, a liquid crystal substrate and the like includes a spin coat method. This is a method for rotating the substrate to be coated onto which a coating solution such as a photo-resist is dropped, thereby spreading, by rotary centrifugal force, the coating solution over the whole surface of the substrate to be coated and evaporating a solvent in the coating solution to form a coating film.
The substrate to be coated such as a wafer is held horizontally on a spin chuck of a vacuum adsorption type. A nozzle for dropping a coating solution such as a resist on the upper surface of the substrate to be coated is provided above the chuck. These elements other than a motor are accommodated in a chamber for preventing the coating solution from being scattered and collecting the scattered coating solution. The chuck is connected to a rotary shaft. The rotary shaft is rotationally supported by the motor.
An air flow inlet is formed in the central part of the upper portion of the chamber. An air flow outlet is formed in the peripheral portion on the lower wall of the chamber. The air flow inlet is connected to a gas feeding device for feeding an inactive carrier gas. Each air flow outlet is connected to an exhausting device through an exhaust duct.
The base end side of the nozzle communicates with a coating solution tank through a coating solution feeding pump.
A housing case for the substrate to be coated is provided in the vicinity of the chamber. A plurality of members to be applied are accommodated in the housing case.
In order to form a coating film such as a resist on the surface of the substrate to be coated by using the apparatus having such a structure, the following procedure is employed.
First of all, a carrier gas is fed from the air feeding device into the chamber and the exhausting device is operated.
Next, the substrate to be coated is taken out, by means of an arm (not shown) from the housing case for the substrate to be coated. Then, the substrate to be coated is fixed onto the chuck through a window openably formed on the peripheral wall of the chamber, and the window is closed. At this time, the carrier gas flows in a direction orthogonal to the upper surface of the substrate to be coated, and flows over the coated surface in a circumferential direction.
Subsequently, the coating solution is dropped in a predetermined amount from the nozzle onto the substrate to be coated.
Then, the rotation of motor is started so that the substrate to be coated is rotated for a constant time.
By thus rotating the substrate to be coated, the coating solution dropped onto the substrate to be coated is spread by centrifugal force over the whole surface of the substrate to be coated and a solvent contained in the coating solution is evaporated. Consequently, a solidxe2x80x94state resist film is formed on the surface of the substrate to be coated.
The thickness of the resist film is occupied by the spread of the coating solution by the centrifugal force in the initial stage of an application process. However, when a viscosity is increased and the fluidity of the coating solution is lowered with the evaporation of the solvent, the thickness of the resist film is occupied by only the amount of evaporation of the solvent. Finally, the application process is terminated when the solvent cannot be evaporated from the gasxe2x80x94liquid interface.
The coating solution scattered from the substrate to be coated during the formation of the coating film is captured on the inner peripheral face of the chamber. Moreover, a gas is fed in an amount suitable for a process work from the gas feeding device. Then, the gas is exhausted in an amount corresponding to the process work by means of the exhausting device through each exhaust duct.
However, the conventional spin coater having the above-mentioned structure has had the following problems.
More specifically, it has been required that an operating (coating) time should be shortened in order to enhance productivity in the field of semiconductor industries which use such an apparatus. By shortening the operating time, the processing amount per unit time is increased to twice if the operating time is reduced by half, and the number of apparatuses is reduced by half if the total of processes is the same. Thus, advantages can be obtained in respect of plant and equipment investment.
In order to shorten the operating time, it is sufficient that the amount of solvent evaporation per unit time is increased. For this purpose, it is proposed that the physical properties of the resist are changed. However, the kind of the physical properties of the solvent are restricted to some extent depending on the easiness of dissolution of a resist resin in consideration of people and environment. Therefore, there is a limit to change the physical properties of the solvent.
On the other hand, it is also proposed that the operating time is shortened by increasing the number of rotations which is the operating condition of the apparatus. However, if the number of rotations is changed, the thickness of a resist film is affected. Therefore, there is naturally a limit. More specifically, if the number of rotations is increased, the centrifugal force is increased. As a result, the thickness of the resist film is reduced. Consequently, it becomes hard to obtain the desired thickness of the resist film.
As described above, the conventional spin coater has had a problem in that it is difficult to shorten the operating time due to conditions such as the matters of the physical properties of a solvent, the matters of the thickness of a coating film and the like, resulting in no contribution to an enhancement in productivity.
Therefore, it is an object of the present invention to provide a coating film forming apparatus which can shorten an operating time without considerably changing the design of the apparatus and the physical properties of a material such as a resist solvent or the like.
A coating film forming apparatus comprising:
a spin coater including a holder for rotatably holding a substrate to be coated and a nozzle provided above the substrate to be coated which is held by the holder for dropping a coating solution onto a surface of the substrate to be coated, and serving to rotate the holder to spread the coating solution over the substrate to be coated by centrifugal force, thereby forming a coating film on the surface of the substrate to be coated;
a chamber for covering the spin coater to form a constant space around the spin coater;
a coating solution feeding pump connected to the nozzle for feeding the coating solution into the chamber;
a coating solution tank coupled to the coating solution feeding pump for storing the coating solution;
a gas introducing pipe connected to the chamber for introducing a gas into the chamber;
a gas exhaust pump connected to the chamber for exhausting a gas from the chamber;
a tank for the substrate to be coated provided on an outside of the chamber for storing the substrate to be coated delivered into the chamber;
a casing including therein the spin coater, the chamber and the tank for the substrate to be coated; and
a temperature control device provided in the casing for controlling a temperature in the casing to be higher than a temperature on an outside of the casing.
According to the present invention, as described above, the operating time can be shortened without considerably changing the design of the apparatus, resulting in a contribution to an enhancement in productivity.